1. Technical Field of the Invention
The present invention relates to a device and a method for fixing an image on recording paper in an image forming apparatus such as a copying machine, facsimile, printer or the like.
2. Description of Related Art
Processing performance of an image forming apparatus such as a printer, facsimile, copying machine or the like for use in an office has been rapidly improved in recent years. Image forming apparatus uses electrophotographic technology to form a toner image on recording paper, and the toner image is fused in a fixing device by applying heat and pressure thereto. A fixing device generally includes a roller heated by a heater and a pressure roller, and recording paper having a toner image thereon is passed through between these rollers, so that toner is melted by heat conduction and fixed on the recording paper.
A pressure-fixing device is also known, in which toner composed of special material, such as paraffin, wax or the like, whose viscosity changes by pressure is squashed under high pressure (normally 15-30 kg/cm) so as to achieve the fixation thereof on recording paper.
As a modification of this pressure-fixing device, Japanese Laid-Open Patent Application No. Sho 52-94139 discloses a fixing device which uses vibration pressure generated in a pair of fixing rollers to fix a toner image on paper. Japanese Laid-Open Patent Application No. Sho 56-99368 discloses a method in which recording paper holding unfixed toner thereon is inserted between an ultrasonic vibrator and a platen to heat and fix the toner by directly applying impact forces. Japanese Laid-Open Utility Model Application No. Sho 60-36663 discloses a fixing method using a heating roller heated by applying ultrasonic vibration. Japanese Laid-Open Patent Application No. Sho 60-91378 discloses a fixing method in which a rotor is provided in a housing and vibration is transmitted to recording paper by the rotor.
In a method using a heating roller heated by a heater, toner is melted to exhibit adhesion so that the toner adheres to recording paper to achieve the fixation thereof. However, most of the applied heat energy is consumed for a loss as radiant heat from the heating roller, a temperature rise of the recording paper, and for evaporation of moisture contained in the recording paper. Thus energy is wasted much more than is used for melting toner, which is the original purpose.
Also, because of its high heat capacity and poor heat transfer efficiency resulting therefrom, it takes long to heat the heating roller, which poses the problem of long standby time after turning on the power. For this reason, various approaches are being adopted to reduce the heat capacity of a fixing device. For example, it has been proposed to provide a stationary heat generator inside a heat resistant film and a pressure roller for pressing the heat generator. However, the heat conduction method inherently involves consumption of energy that is not used for the fixing purpose as described above, and in this regard a reduction in required energy is achieved only to a limited extent. Moreover, a temperature rise inside the device is unavoidable because of the heat source disposed within the device.
The pressure-fixing method has advantages that it is energy-saving, and does not need any standby time. On the other hand, because of the use of high pressure, problems arise that the device is upsized, thereby increasing the weight and cost, strong gloss remains on an image, impact noises occur when recording paper is discharged and so forth.
A fixing device utilizing impact pressure such as ultrasonic vibration has another problem of early deterioration of bearings for supporting rollers, to which vibration is transmitted. There is also a problem of noises that may occur due to ultrasonic vibration. Application of ultrasonic vibration often causes toner to scatter, whereby image quality may be degraded. For these reasons, the ultrasonic vibration method has not yet been put in practical use.
The present invention has been devised in light of the above-described problems encountered by the prior art, and it is an object of the invention to provide a compact image fixing device using ultrasonic vibration which achieves high energy efficiency and high image quality, and an image fixing method using the same.
To achieve the above object, an image fixing method according to one embodiment of the present invention includes the steps of generating ultrasonic vibration, moving recording paper while bringing an image forming surface of the recording paper into close contact with an outer peripheral surface of an endless belt coated with a rubber layer and transmitting the ultrasonic vibration to the image forming surface of the traveling recording paper via the belt.
A fixing method according to another embodiment of the present invention includes the steps of generating ultrasonic vibration, converting the generated ultrasonic vibration to progressive waves proceeding in a direction generally in parallel to the recording paper surface, pressing a colorant forming an image between the recording paper and a presser member and transmitting vibration of the progressive waves to the colorant.
These and other objects and characteristics of the present invention will become further clear from the following description with reference to the accompanying drawings.